1. Field of the Invention
This invention relates to a dielectric film comprising a dielectric material including a piezoelectric material, a piezoelectric element, a liquid-jet apparatus, a method for producing a dielectric film, a method for producing a piezoelectric element having a piezoelectric film comprising a piezoelectric material, and a method for producing a liquid-jet head.
2. Description of the Related Art
A piezoelectric element used in a liquid-jet head, etc. is an element comprising a piezoelectric film sandwiched between two electrodes, the piezoelectric film comprising a piezoelectric material having an electromechanical conversion function. The piezoelectric film is composed of, for example, a crystallized piezoelectric ceramic.
An example of a liquid-jet head using such a piezoelectric element is an ink-jet recording head in which a portion of a pressure generating chamber communicating with a nozzle orifice for ejection of ink droplets is constituted of a vibration plate, and the vibration plate is deformed by the piezoelectric element to pressurize ink in the pressure generating chamber, thereby ejecting ink droplets from the nozzle orifice. Two types of ink-jet recording heads are put into practical use. One of them uses a piezoelectric actuator in a longitudinal vibration mode which expands and contracts in the axial direction of the piezoelectric element. The other uses a piezoelectric actuator in a flexural vibration mode. As the ink-jet recording head using the actuator in the flexural vibration mode, there is known, for example, an ink-jet recording head having a piezoelectric element which has been formed by forming a uniform piezoelectric layer over the entire surface of the vibration plate by a film-forming technology, and cutting the piezoelectric layer into forms corresponding to the pressure generating chambers by lithography to form the piezoelectric element independently for each pressure generating chamber.
The so-called sol-gel process is known as a method for producing the piezoelectric layer constituting the piezoelectric element. According to this method, a sol of an organometallic compound is coated on a substrate having a lower electrode formed thereon, followed by drying and gelling (degreasing) the coating to form a piezoelectric precursor film. This step of forming the precursor film is performed at least once. Then, the resulting precursor film is heat-treated at a high temperature for crystallization. These steps are repeated a plurality of times to prepare a piezoelectric layer (piezoelectric thin film) of a predetermined thickness.
The so-called MOD (metal-organic decomposition) method is known as another method for producing the piezoelectric layer constituting the piezoelectric element. This method generally comprises dissolving an organometallic compound, such as a metal alkoxide, in an alcohol, adding a hydrolysis inhibitor or the like to obtain a colloidal solution, coating the colloidal solution on a suitable material, then drying and sintering the coating to form the piezoelectric layer.
The conventional methods for producing the piezoelectric layer are disclosed, for example, on Japanese Patent Application Laid-Open No. 1997-223830 (pages 4 to 6) and Laid-Open No. 1994-005946. According to these methods, a piezoelectric layer of 1 μm or more in thickness can be formed relatively satisfactorily, and the occurrence of cracks can be prevented. However, the methods pose the problems that the crystalline state of the piezoelectric layer, such as the crystal grain size or orientation, is difficult to control, and a piezoelectric layer having desired characteristics is not obtained. Such problems are not limited to the piezoelectric film comprising the piezoelectric material for use in the piezoelectric element, etc. of the liquid-jet head, but are similarly encountered with dielectric films comprising other dielectric materials.